The invention relates to a high pressure ball valve, and more particularly to Kelly cocks used in oil well drilling.
In a rotary drilling rig, an engine turns a round flat table having a square aperture therethrough. The table rotates a square piece of pipe, the Kelly, that extends through the aperture and threadably engages the remainder of the drill string. A Kelly cock is a valve mechanism housed within a cylindrical pipe that is threadably engaged to the drill string above or below the Kelly. The Kelly cock permits the opening and closing of the drill string to the drilling fluid, "mud", which is pumped under high pressure from above the Kelly down the drill string, to the drill bit. The Kelly cock also permits the string to be closed to the natural gas or oil which may on occasion emanate under high pressure from the ground. The Kelly cock must therefore create a tight seal when closed, withstanding tremendous internal pressure of at least 10,000 psi.
Various types of valves have been employed as Kelly cocks, including ball valves. For example, the ball valve manufactured by Hydril Company, Los Angeles, Calif., has a ball rotatably mounted between a fixed upper seat and a spring-loaded lower seat. The ball has a slot which receives a wrench plug for rotating the ball between opened and closed positions. Loading of the valve requires the use of a tool which is inserted from the box end of the casing to compress the ball against the spring below. With the spring compressed, the upper seat is locked in sealing contact with the ball by means of four locking segments which are positioned within a groove in the casing and form an annular shoulder which abuts the upper seat, fixing it with respect to axial movement.
While an improvement over many prior valves, the Hydril valve still suffers from several disadvantages. First, loading the valve requires a tool which must be inserted from the box end into the casing. Secondly, the valve has at least three retaining rings including the locking segments located above the upper seat which present an exposed, uneven surface making them subject to abrasion and corrosion from the drilling fluids.
There is therefore a need for a high pressure Kelly cock valve which can be quickly and easily loaded, and which provides control over the well flow with minimal corrosion and abrasion of parts.